"L7" = "square"2He then held up his hands to demonstrate, the one hand making an L and the other making a 7 (well sort of — the top horizontal is perhaps disproportionately long, but close enough). And what's the shape in the middle? A square! Dig it, man, dig it.
1 "Slang of the Day" implies that this will be a daily feature. I should make clear that this most certainly won't be the case. We have ventured into slang territory in the past though at wildly sporadic intervals. But "Slang of the Wildly Sporadic Interval" just doesn't roll off the tongue. ("Roll of the tongue" — there's a funny saying.)
2 In the beatnik/hippie sense of "uncool", so the lyric is actually perfectly meaningful: Let's not be lame. Let's get out on the dance floor. (I'll note that this is the second time in a few days that we've used the term "square" in this way.)